Satellite tracking systems can be very helpful for monitoring objects, especially when tracking highly mobile objects which move through remote areas or over great distances. For example, satellite tracking systems can be very useful when tracking the movement of shipping containers, trucks, ships, airplanes, and similar objects which may travel across an ocean or continent. In these circumstances, it would be difficult, if not impossible, to coordinate observers for monitoring the object at regular intervals. Furthermore, it is typically impractical to communicate directly with a tracking tag placed on the object due to the distances involved, the size and cost of the transmitters, and the energy required for transmission. Thus, as satellite technology matures, tracking systems are being developed for communicating with tracking tags by a satellite link.
Although there are a number of satellite tracking systems and devices in the prior art, the energy consumed by current tracking tags can impair the reliability of the tracking system or force a compromise in tracking accuracy. Energy consumption can be a problem because the tags typically operate in remote areas where a reliable external power source may not be available, yet the tags require energy to gather data from sensors and transmit information to a satellite. For this reason, tags are generally provided with batteries. However, the battery power may be exhausted prematurely depending on the duration of the tracking period, the frequency of tag transmissions, and the quantity and type of information transmitted. In some cases greater battery capacity can be provided, but this solution increases the size and cost of the tag. Moreover, even a large battery supply can be exhausted if the surveillance period is unexpectedly long. For instance, when tracking a shipping container, the shipment may be delayed, diverted, or stolen. In these situations, the tracking system may have its greatest utility, however, the limited battery capacity jeopardizes the tracking process.
To address this problem, some tags have been developed to minimize power consumption by collecting and transmitting data at pre-selected intervals according to an internal timer. This solution, however, can reduce tracking accuracy if information is not received with sufficient regularity. In addition, users cannot adjust the time interval between tag transmissions when unexpected events occur. For example, the pre-selected intervals cannot be modified to provide more frequent transmissions if the tag and object are diverted, nor can the intervals be modified for less frequent transmissions if battery capacity is low. To overcome these problems, some timer operated tags have been developed with two-way communication capability which allow remote adjustment of tag operations, such as Maine (U.S. Pat. No. 5,666,647). These tags, however, still rely on battery power when operational.
In view of the above considerations, a primary object of the present invention is to provide a tracking tag which is connectable to an external power supply for conserving battery power when an external power supply is available.
Another object of the present invention is to provide a microprocessor for recognizing the availability of an external power source and for connecting and disconnecting the tag from a battery power supply depending on the availability of an external power supply.
Yet another object of the present invention is to provide a tag with dual mode operation capability in which the tag is continuously activated in a full power mode when an external power source is available, and intermittently activated in a battery conserving mode when battery powered.
Still another object of the present invention is to provide two-way radio frequency communication capability so that both modes of tag operation can be remotely adjusted to conserve energy, to increase the frequency of tag communications, or to change the content of the information transmitted by the tag.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.